As the method of patterning a metal film such as thin-film electrodes etc., there are two general methods, that is, (a) a method in which a photoresist film is formed by applying a radiation sensitive resin composition onto a metal film, subjected to pattern exposure and then developed to form a resist pattern, followed by wet or dry etching, and (b) a lift-off method in which a photoresist film on a substrate is subjected to pattern exposure and developed, and then the substrate having the resist pattern thus formed is vapor-deposited with a metal, followed by releasing and removing the resist pattern. In this lift-off method, vapor-deposition of a metal onto the substrate having the resist pattern thereon brings about formation of vapor-deposited films on the resist pattern and the bare substrate, and it is well-known that if a profile of the resist pattern has an overhung or reverse-tapered shape, the vapor-deposited film formed on the substrate becomes discontinuous with the vapor-deposited film formed on the resist pattern, thus being preferable in forming electrodes.
A wide variety of positive-or negative-working radiation sensitive resin compositions have been used for forming photoresist films in production of semiconductor integrated circuits such as ultra-LSI etc. or production of liquid crystal display panels for LCD. However, the number of radiation sensitive resin compositions known to be preferable for the lift-off method described above is limited. A reverse tapered resist pattern, therefore, has been formed by selecting suitable radiation sensitive resin composition from known compositions and setting special processing conditions, for example, regulating exposure conditions or development conditions. Further, even if a reverse tapered resist pattern is successfully obtained, the resist pattern usually has a problem of pattern profile or is problematic due to inferiority in characteristics of the resist film such as heat resistance or hygroscopic property of the resist.
Meanwhile, the separate coating of RGB organic EL medias or formation of electrodes in a 3-colors independent luminescent system has been carried out in recent years in production of organic EL display panels. In this field, there is an increasing need for materials capable of forming a reverse tapered resist pattern with an excellent profile and good heat-resistance, low water absorption and high electrical insulation as an insulating member between cathodes. The reasons are those described below. First, the organic EL display panel usually manufactured by following processes. That is, on a plurality of first parallel and striped electrodes provided on a substrate, a plurality of insulating films and barrier plates are arranged at predetermined intervals on and in a direction perpendicular to the first electrodes. Organic EL medias corresponding to luminescent colors such as red (R), green (G), blue (B) etc. are vapor-deposited through a vapor-deposition mask having a predetermined cut-out pattern onto the bare regions of the first electrodes and the barrier plates. Then second electrodes are formed on the organic EL medias by vapor-deposition of a highly electrically conductive metal on the whole surface including the surfaces of the organic EL medias and barrier plates. Thereafter, one side of the substrate on which the barrier plates and organic EL medias have been formed is sealed with glass plate via an adhesive. Inert gas etc. are filled in the hollow space formed by the glass plate, the adhesive and the substrate to shield from moisture in the outside, thus completing the production of the organic EL panel. If the barrier plates have reverse-tapered form at the time of producing the second electrodes, the metal layers vapor-deposited on the barrier plates become discontinuous with the metal layers (i.e. the second electrodes) on the organic EL media, thus preventing electrical connection or short-circuit between the adjacent two electrodes. Further, since the EL luminescent devices are easily damaged by water, solvent components etc., low water absorption materials are desired as that of a barrier plate (JP-A 10-312886). Furthermore, since the barrier plate material is subjected to degassing treatment at high temperatures for removing the residual solvent in the barrier plate material, the material which is not deformed by heating is preferable in order to prevent short-circuit between adjacent electrodes as the material for barrier plate member.
As a radiation sensitive resin composition for lift-off and the method of forming a pattern by lift-off, a negative-working radiation sensitive resin composition containing a compound absorbing exposure light and a method of using the composition (JP Patent No. 2989064) etc. are known.
From the viewpoint of improving heat resistance, there are known that a radiation sensitive resin composition comprising a polymer obtained by ring-opening polymerization of a norbornene derivative and an aromatic bis-azide compound (JP-A 60-111240), a radiation sensitive resin composition comprising a photopolymerization initiator, a sensitizer and a copolymerizable monomer (JP-A 61-23618) etc. In addition, a novolak-based thermosetting resin (JP-A 5-178951), a composition comprising a cyclic olefinic resin and an aromatic bis-azide compound (JP-A 7-92668) have also been proposed. Heat resistance is improved by these prior art techniques, but the compositions described therein need further improvements as the radiation sensitive resin composition used in the method of forming a pattern by the lift-off method, or for a barrier plate materials between cathodes in organic EL panels.
In view of the circumstances described above, the object of the present invention is to provide a method of forming a resist pattern, a method of forming a good metal film pattern by the lift-off method, and an, insulating member in organic EL display panels free of these problems in the prior art. That is, the object of the present invention is to provide a method of forming a reverse tapered resist pattern with an excellent pattern shape, excellent heat resistance, and low water absorption, a method of forming a metal film pattern by using said resist pattern in the lift-off method, and an insulating member in organic EL panels, which comprises said resist pattern.